Hertz (Hz) is a unit of frequency and is used to indicate the frequency of sound waves and electromagnetic waves, etc. A single wave or vibration cycle in one second is represented as 1Hz.
This unit is often used in connection with computers to indicate the clock frequency, or the processing speed, of a CPU (Central Processing Unit). A clock frequency is the number of opportunities the CPU can process something in a second. For example, if the clock frequency is 1Hz this would be once a second, if it is 1MHz (megahertz) one million times per second, and if it is 1GHz (gigahertz) one billion times per second. Therefore, a 3GHz CPU is capable of performing 3 billion processes per second. (Clock frequency is one means of representing the performance of a CPU but performance will also depend on the type of CPU.)
The sampling rate of audio data is also shown using this unit. Analog sounds are digitized through processes known as sampling and quantization. For instance, the sampling rate of a typical music CD (CD-DA) is 44,100Hz. With sound, the frequency determines the pitch. A low frequency sound has a low pitch whereas a high frequency sound has a high pitch. The range of sound that is audible to the human ear is between 20Hz and 20,000Hz, which means that the highest pitch we can hear oscillates at a rate of 20,000 times a second. When digitizing analog sound, it is said that sound must be measured at least twice the cycle of the frequency of the original sound, so to digitize sound which is oscillating 20,000 times per second, it is necessary to take 40,000 samples or more per second. Therefore, a sampling rate of 44,100Hz means the audio data was measured 44,100 times a second.
44,100Hz is one of the standard sampling rates used when recording sound to be edited on a computer.
- "System Properties" window on Windows XP (top) and "About This Mac" window on Mac OS X (bottom). Clock frequency can also be confirmed on this screen. Frequency units will be in GHz.
- Several editing and recording sampling rates can be selected on an audio editing software (Audacity in the example above). 44,100Hz is one of the standard sampling rates used in digital recording devices.